Boston Celtics star Jaylen Brown has agreed to a five-year, $304m supermax contract extension which would be the most valuable deal in NBA history.

Brown’s agent, Jason Glushon, said he and the player met with Celtics management on Sunday to finalize the contract, which will keep the 26-year-old with the team until the end of the 2028-9 season.

The two-time All-Star averaged career highs of 26.6 points, 6.9 rebounds and 3.5 assists last season. But those numbers went down in the playoffs, when the Celtics lost to the Miami Heat in the Eastern Conference finals; in Game 7 Brown had 19 points on eight of 23 shooting, making just one of nine three-point attempts. By virtue of making the All-NBA second team – his first such honor in his career – he was eligible for the supermax extension.

The Celtics picked Brown with the third overall selection in the 2016 draft. They have made the playoffs every season since, although he is not widely considered a Top 10 player in the league. Indeed, most observers do not even think Brown is the best player at the Celtics; most would give that honor to Jayson Tatum, who is a four-time All-Star and was named to the NBA first-team this year. Tatum will be eligible for a supermax extension next year.

Brown is a shrewd businessman and has also spoken about social issues.

“Sports is a mechanism of control,” he told the Guardian in 2018. “If people didn’t have sports they would be a lot more disappointed with their role in society. There would be a lot more anger or stress about the injustice of poverty and hunger. Sports is a way to channel our energy into something positive. Without sports who knows what half of these kids would be doing?”